1. Field of the Invention
The present invention relates generally to a communication system, and in particular, to a method and apparatus for receiving data in a communication system using a Hybrid Automatic Repeat reQuest (HARQ) scheme.
2. Description of the Related Art
An error control scheme used in communication systems can be roughly divided into a Forward Error Correction (FEC) scheme and an Automatic Repeat reQuest (ARQ) scheme. FEC corrects errors in received data using codes having error correction capability, and is used when there is no feedback channel over which an Acknowledgement (ACK)/Non-Acknowledgement (NACK) message indicating success/failure in data transmission is to be transmitted to a transmitter. ARQ detects errors in received information using Cyclic Redundancy Check (CRC) codes having high error correction capability, and sends a retransmission request to a transmitter over a feedback channel upon detecting the errors. In FEC, if a receiver fails in error correction, erroneous data may be delivered to the user undesirably. Therefore, when a high-reliability system is realized with FEC, powerful codes capable of correcting a great number of errors are used, causing an increase in decoding complexity and thus making it difficult to realize the system. Compared with FEC, ARQ is low in complexity and high in reliability, but suffers from an abrupt decrease in information throughput as a channel error rate increases. To solve the problems of the above two schemes, the HARQ scheme has been proposed by combining ARQ and FEC.
HARQ can be classified into several schemes according to format of retransmission packets, a combining method of an exiting packet and a retransmitted packet, and presence/absence of the combining method. In other words, HARQ can be classified according to whether the retransmission packet is equal to the existing packet. Even if the retransmission packet is not equal to the existing packet, HARQ can be classified according to whether a part of the retransmission packet is equal to the existing packet. In addition, HARQ can be classified according to whether the retransmission packet is combined with the existing packet. The HARQ scheme generally combines the existing packet with the retransmitted packet, and decodes the combined packet. However, a HARQ scheme has not proposed yet having any detailed method of combining a defective packet with a retransmitted packet.